Step-by-step explanation:
when the order of the picked subset does NOT matter, we are calling this combinations.
when the order DOES matter, we are dealing with permutations.
in our case here the order does matter, as we are defining not only who is going to bat, but also in what sequence.
so, we are dealing with the permutations
P(13, 9) = 13! / (13 - 9)! = 13!/4! =
= 13×12×11×10×9×8×7×6×5×4×3×2/(4×3×2) =
= 13×12×11×10×9×8×7×6×5 = 259,459,200 ways
